If there was an index that ranked the most important little-understood countries, Indonesia would surely come first.

With 250m people, it is the fourth most populous nation, with more Muslims than any other. The only G20 member in southeast Asia, it is the world’s tenth-largest economy and is growing at a steady clip. And next week it will see the conclusion of a presidential election campaign that, while boisterous, puts the dictatorships, juntas and sham democracies dominating much of Asia to shame.

Yet many people would struggle to locate it on a map. Much international media coverage of Indonesia revolves around natural disasters and “weird world” stories of smoking toddlers, people being killed by exotic animals or clumsy officials shooting off their mouths about the need for teenage virginity tests.

Literature on this rising nation has been similarly lacking over the past decade. There have been plenty of micro-studies by academics but few attempts to paint a broad picture of the country and its dramatic, mostly successful transformation since the fall of long-ruling dictator Suharto in 1998.

Elizabeth Pisani, a journalist turned epidemiologist, begins to address this imbalance with Indonesia Etc. Pisani has been working in Indonesia on and off since she was sent there as a rookie Reuters reporter in 1988. Now, after criss-crossing the country, she aims to elucidate the contrasts, quirks and contradictions of this vast archipelago with a sharply written, politically infused travelogue.

The title comes from Indonesia’s wonderfully vague declaration of independence from Dutch rule in August 1945, which said that “Matters relating to the transfer of power etc. will be executed carefully and as soon as possible”.

As she meanders through Indonesia’s heartlands and rarely visited outlying areas, Pisani sketches out how this country of thousands of islands, hundreds of languages and ethnic groups, six official religions (Islam, Protestantism, Catholicism, Hinduism, Buddhism and Confucianism) and many local cults was “melded together by the cupidity of Dutch merchants”.

On the sleepy island of Sumba, she watches dogs being sacrificed to see if a couple are suitable for marriage and takes tea with a corpse, in a traditional pre-burial rite. Nominally Christian, islanders mix their official religion with local belief systems and, writes Pisani, are “guided more by what they read in the entrails of a chicken then by what they read in the Bible”.

That contrasts starkly with her brief stops in the capital Jakarta, a booming icon of rapid but uneven development, where she hobnobs with her artist, journalist and expat friends at bars built in the midst of sprawling slums. “Different groups are essentially living at different points in human history,” she writes.

What then keeps this accidental nation together? Pisani nods towards the power of patronage networks – and the corruption that follows – as well as to a new wave of consumption that is ensuring that Indonesians from Aceh to Papua are increasingly eating the same instant noodles, watching the same TV advertisements and smoking the same cigarettes.

Occasionally, she overreaches in her pursuit of the colourful phrase (she describes a town on the island of Flores as smelling of “stale sex” after the meat from a whale hunt is hung out to dry) and her insistence on “just saying yes” to new experiences can give her the air of a worthier-than-thou backpacker. But her regular comic mishaps, punchy insights and journalist’s eye for the telling detail more than compensate.

After puzzling over how to reconcile the many faces of Indonesia, Pisani concludes that the beauty of this country lies in the freedom it gives its people to live their lives how they wish. As one poor farmer that she meets in Sumatra puts it, reflecting on the legendary traffic jams in the capital: “How is that better than sitting under a tree?”